Despite this week's drama series win at the Emmys, NBC's "The West Wing" returns at 9 tonight following its most uneven season to date. It's an assessment series creator Aaron Sorkin probably wouldn't debate.

Martin Sheen waits between takes during filming of "The West Wing" at a farm near Volant. (John Beale, Post-Gazette)

"The West Wing"

When: 9 tonight on NBC.

Starring: Martin Sheen

"For me, the most exciting thing about this season is it's no longer last season," he said in a recent teleconference. "Last season was very difficult for a number of reasons."

Primarily, he said, the notion of fictional heroes, including the characters on "The West Wing," was in bad taste after Sept. 11. Sorkin also had no interest in stories of Democrats fighting with Republicans and the White House fighting with Congress.

"Sept. 11 was one of those rare moments when things are black and white, when there's a moral absolute, and I felt, frankly, like last season was a continual search for what I wasn't doing that makes the show work," he said. "One week I'd feel like, well, I'm back, I can write now. And the next week would be a train wreck, and I just couldn't do it. All year long it felt like we were doing something wrong and we couldn't put our finger on it. It's a year later, and when I came back to begin writing the show, I didn't feel that anymore."

Although the threat of terrorism is now "part of the water supply" in American culture and on "The West Wing," Sorkin said, the show has its sense of fun back. That's expected to be on display in the two-hour fourth-season premiere, tonight's "20 Hours in America," which was filmed in part in Western Pennsylvania (doubling for Indiana).

The episode begins with President Bartlet (Martin Sheen) at a campaign rally on a soybean farm. Communications director Toby Ziegler (Richard Schiff), deputy chief of staff Josh Lyman (Bradley Whitford) and his assistant, Donna Moss (Janel Moloney), get left behind on the farm and spend much of the season premiere trying to catch up with the president's motorcade.

A temporary production office was set up in Pittsburgh for the filming, which lasted a week and a day.

"Did we treat your town OK?" Sorkin asked, adding he got positive reports from the show's cast and crew. "The people couldn't have been nicer, and the location couldn't have been more beautiful. The footage looks terrific. It was a very, very successful trip."

Sorkin said the "Planes, Trains and Automobiles"-type story was inspired by an assistant to President Clinton who had the same job as Charlie (Dule Hill) on "The West Wing."

"A couple years ago, he told Dule that motorcades leave when the president gets in the car. It doesn't wait for anybody. The Secret Service can't have the president sitting there, so it's not uncommon to have people left behind. He talked about running in to buy a postcard and coming out and there was nothing there. That was too good to be true, so I wrote an episode about it."

Bartlet's campaign will culminate in an election episode in early November, and though it's a safe bet he'll win, Schiff said, it won't be a cakewalk.

"I've always said, the real brilliant way to go out would be to lose," Schiff said last month during filming on a Lawrence County farm. "We would go out on top of the ratings, we'd shock the TV world. Then they could pick up sequels. Josh and Donna could do a sitcom. Leo would be the next Lou Grant, and I'd go back to off-off-off-off-off-Broadway. Artistically, you've got to admit...."

Schiff hinted at an upcoming episode about a debate between presidential candidates, but he was less sure what will follow Bartlet's re-election.

"I think the normal re-election cycle is, we win the election and then the scandals start happening one by one," he said. "I don't know if we'll repeat that, but in real life, you win the election and that's when all the dirt gets uncovered, right?"

This season, Sorkin will have to lay the groundwork for the March departure of Sam Seaborn, unless actor Rob Lowe opts to stay with the series, which seems unlikely.

"In terms of how I'm proceeding with the writing, there is a plan in place. Sam Seaborn isn't going to die. The door is always going to be open."

Sorkin said he hopes Lowe will stay, but that if he leaves, it will add to the realism of the show. As it is, real top presidential staffers rarely stay in the job as long as the characters on "West Wing" have.

"I don't know any core White House staff that has lasted this long," he said. "Ordinarily, that kind of realism is something I'd obviously sacrifice to hang onto an extraordinary group of actors and take heart in the fact that 'M*A*S*H' ran three times as long as the war it portrayed."